<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button>发送请求</button>
</body>
<script>
  const btn = document.querySelector('button')
  btn.onclick = function () {
    const xhr = new XMLHttpRequest()
    xhr.open('GET', 'http://127.0.0.1:8000/cors-server')
    xhr.send()
    xhr.onreadystatechange = function(){
      if(xhr.readyState === 4) {
        if(xhr.status >= 200 && xhr.status < 300) {
          console.log(xhr.response)
        }
      }
    }
  }
</script>
</html>